Aluminum casting process



ALUMINUM CASTING PROCESS Walter E. Jominy, Detroit, and John H. Olsonand Robert B. Boswell, Birmingham, Mich., assignors to ChryslerCorporation, Highland Park, Mich, a corporation of Delaware No Drawing.Original application Mar. 23, 1953, Ser. No. 344,190, now Patent No.2,881,491, dated Apr. 14, 1959. Divided and this application Dec. 9,1957, Ser. No. 701,340

6 Claims. (Cl. 22-204) This invention relates to a process for formingcomposite or duplex metal structures, specifically aluminumferrous metalstructures by casting a layer of hot molten aluminum or its alloys to apreformed ferrous metal body -or base such as of steel or iron andforming an integral alloy bond therewith. This application is a divisionof our copending application Serial No. 344,190 filed March 23, 1953,now Patent No. 2,881,491, granted April 14, 1959.

More particularly, our invention relates to such a process in which afused flux of suitable salts and of such viscosity as to possess ease orfreedom of flow, that is to say, a liquid or fluent flux, is employed toeffect the alloy bonding of the aluminum with the ferrous metal.

The casting of aluminum to ferrous metal in a mold presents problems notencountered in the conventional aluminum coating procedures where aflux-treated ferrous member is immersed in a bath of the hot moltenaluminum to form a coating or predetermined layer of the latter thereon.In the mold casting process, the ferrous member instead of beingimmersed in a large mass of constantly heated molten aluminum, is placedin a suitable mold into which molten aluminum ladled from the furnace ispoured. A heavy cast layer of aluminum of substantial thickness isformed integral with the ferrous metal body and is of a thickness manytimes that obtained by coating steel with aluminum by immersion ordipping. Necessarily a loss of heat occurs on transfer, and a longertime interval transpires in the casting process during which the fluxmay cool before the aluminum reaches the fluxtreated ferrous metal andfills the mold. Problems of heat exchange, therefore, arise which arenot usual in a coating procedure. Moreover, in a dip coating process, ifa suitable ductile alloy layer is to be obtained with the ferrous metal,the molten aluminum where prepared from substantially pure ingot, mustusually be employed at a temperature immediately above its melting point(1220 F.). In a mold casting process, in order to secure an alloy bond,the temperature of the molten aluminum must be considerably higher thanits melting point and higher than the temperatures usually used in a dipcoating process. We have found that this feature makes possible agreater latitude in the temperature of the aluminum in operation.

Furthermore, it has heretofore been proposed to cast aluminum to aferrous metal body in a mold by a procedure wherein the ferrous body isfirst given a hot dip or flash coating of the aluminum. According tothis process, the ferrous body is first dipped in a bath of moltenaluminum and then transferred to a mold into which molten aluminum ofthe bath is then poured so that it contacts the flash-coated surface toform an alloy bond with the ferrous body.

The described process is at best only partially successful and has anumber of disadvantages. Unless the interior surfaces of the member aremasked with a suitable tinuous alloy bond with the ferrous metal.

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graphite washto protect them from the aluminum bath they will alloy withthe aluminum and leave undesired aluminiun surfaces that will have to besubseqently machined off. Also oxidized areas form upon the ferrousmetal surfaces during heating of the ferrous body when it is immersed inthe aluminum bath. The molten aluminum does not wet the ferrous surfacesin the oxidized areas, this even when the surfaces are scraped to breakthrough the oxide layers, and as a result no alloy bond is obtainablebetween the cast aluminum and ferrous surfaces in these unwetted areas.Stated otherwise, it is difiicult by the recited process to obtain acontinuous aluminum flash coating, and the cast layer of aluminumsubsequently formed is not always provided with a con- Moreover, duringflash coating of the ferrous body, the molten aluminum of the bathdissolves some of the ferrous metal. This causes particles of a hardhigh melting point iron aluminum alloy to accumulate in the bath. Inorder to settle out these particles, the bath must be allowed to stand.This requires a holding period making extra furnace capacity necessary.If the particles are not permitted to settle out, they may be carriedwith the molten aluminum of the bath to the molds when it issubsequently poured to make the cast layers. There they form hard spotswhich make machining of the cast layer difficult.

In seeking a more suitable procedure for successfully casting aluminumor its alloys to ferrous metal bodies in a mold, other methods wereconsidered and it was found that a continuous alloy bond between thecast aluminum and ferrous metal may be obtained by a process utilizing afluent fused flux composition. It was noted, however, that certainingredients are essential to the composition and that proper proportionsthereof, the temperature conditions under which the composition isemployed, and

the time interval between removal of the ferrous body from the flux andthe start of pouring of the molten aluminum are of a critical nature andnecessary of careful control in order to obtain good wetting propertiesand an acceptable continuous alloy bond between the aluminum and theferrous metal.

For example, careful selection of the character of the flux compositionand of the operating temperatures is es sential to avoid thin spots inthe protective flux layer or more extensive incomplete wetting of theferrous metal surfaces, either of which will permit oxidation of theferrous metal. Moreover, if the flux is too viscous, an excessive amountwill adhere to the ferrous surface and may not be easily washed out bythe molten aluminum during casting. If the flux is not completely washedoff, any remainders are likely to produce unbonded spots between thealuminum and steel which will also be subject to subsequent corrosion.Improper temperature control of the operations, improper compositions,and too long a time interval between fluxing and pouring also contributeto solidification of the flux on the steel before pouring of thealuminum takes place. Where this occurs, the flux adheres to the ferrousmetal surface with considerable adhesion and must be melted by thealuminum before it can be washed off. This is unlikely to be complete.

Accordingly, it is an object of our invention to provide a process forcasting aluminum to ferrous metal bodies in a mold which utilizes afused flux composition that provides good wetting properties relative tothe ferrous metal surfaces to which the aluminum is to be alloy bondedand which will provide a layer of the flux of sufficient thickness tocompletely blanket these surfaces to effectively protect them fromoxidation prior to pouring of the aluminum.

Another object is to provide such a process in which the ferrous metalsurfaces to which aluminum is to be directly bonded by casting are givena layer of fluent fused flux composition of suflicient viscosity to beadherent and that will maintain its freely flowable character prior toand during pouring of the molten aluminum such that the latter can pushthe flux ahead of it, i.e. float the flux on top of it without leavingflux remainders as its level changes in the mold.

A further object is to provide such a process wherein the poured moltenaluminum will completely wet and cover the ferrous metal surfaces as itremoves the flux, and form a complete and continuous alloy bondtherewith.

An additional object is to provide fused flux compositions operable inthe aforesaid processes.

Another object is to provide a control system for compensating for lossof essential ingredients during operations.

Other objects will become apparent from the following description of thepreferred embodiments of our invention. For the purpose of illustrationonly, we will describe our invention as applied to casting collars ormuffs of aluminum on steel sleeves, and in particular to the making offorged alloy steel barrels with an aluminum muff which is to besubsequently machined to provide cooling fins for these barrels whichare to form the cylinders in air-cooled tank engines.

In carrying out our invention, we have discovered that the esssentialbasic ingredients of the fused flux composition are sodium chloride(NaCl), potassium chloride (KCl), and natural Greenland cryolite (sodiumaluminum fluorideNa AlF When used in proper amounts, these salts makepossible a flux composition having excellent fluxing properties. Tothese should preferably be added anhydrous zinc chloride (ZnCl which wehave discovered considerably improves the mixture by increasing itsviscosity. Other alkali salts such as calcium chloride (CaCl or otherfluorides such as synthetic or reduction grade cryolite may optionallybe included by addition or substitution but in limited amounts as willbe hereinafter evident.

Broadly speaking, by our process, the ferrous metal members afterinitial treatment by known or hereinafter described procedures to insurethat their surfaces are clean and free from impurities, are immersed ina hot fluent fused flux bath (940-1180 F. melting point) having atemperature preferably substantially not less than 1340 F. andpreferably not exceeding substantially 1450" F.

The amount of the essential ingredients to use may vary within certainpermissible limits depending upon the character of parts being treatedand the time elapsing between fluxing and start of pouring of thealuminum. For example, in some operations especially where the parts tobe treated have a relatively small surface area and can be rapidlyprocessed between flux treatment and casting, for example within 30seconds, the bath may contain a molten mixture of the followingessential ingredients in about the amounts stated:

Parts by weight Sodium chloride 7 to 40 Potassium chloride -c 24 to 44Natural Greenland cryolite 9 to 25 Zinc chloride to 34 Although no zincchloride has been been used with success in certain compositions, it isgenerally found expedient to use at least a small amount of thisingredient for its viscosity control feature. However, if the amount ofzinc chloride exceeds about 25% by weight, excessive fuming may occur atthe higher temperatures and must be controlled. Moreover, cryolite above25% causes excessive sludging.

Where the ferrous metal surfaces to be treated are large and are notideal for bonding, or where a greater time period is required, forinstance up to about 40 secae'maso v ends, between fluxing and casting,a somewhat closer range of ingredients is desirable. In such cases thefollowing range of essential ingredients will be found to be preferable:

Parts by weights Sodium chloride 25 to 40 Potassium chloride 25 to 40'Natural Greenland cryolite 9 to 25 Zinc chloride 10 to 30 The parts arepreferably kept immersed in the flux bath at least until they attain atemperature about that of the bath temperature and are then removed.Such time of immersion is sufficient to provide a substantial layer ofthe fluent flux on the sleeves or barrels, and to reanelt the initialsolid flux envelope which forms on the sleeves or barrels when initiallyimmersed. The actual time of immersion will, of course, vary with thesize and composition of the flux bath, and the size and physicalcharacter of the ferrous member to be treated and the temperature drop,if any, of the bath. If the sleeves or barrels have been previouslyhardened and tempered to a specified degree of hardness, it is preferredthat the immersion time be kept to a minimum in order to maintain thehardness value close to the original hardness of the member at theconclusion of the casting operation. It has been found that incommercial practice using large flux baths and treating large heattreated barrels of approximately wall thickness, about 3 to 4 minutes(usually about 3 /2 minutes) in the flux bath is sufficient for adequateflux treatment.

When treated in the foregoing manner, the ferrous sleeves or barrelswill have a layer of fluent flux composition of sufficient thickness toenable then when placed immediately after fluxing in molds into whichmolten aluminum (1220 F. melting point) at a temperature substantiallybetween 1325 F. and 1425 F. and prefer ably between 1350 F. and 1400 F.is poured, to obtain a good alloy bond between the ferrous metalsurfaces and the aluminum when the latter is solidified.

The time interval between removal of the flux-coated sleeves from theflux bath and start of pouring of the molten aluminum is also essentialof control. in general, the time interval should be short enough toavoid cooling down of the sleeve to a point where substantial freezingor solidification of the flux takes place, or stated otherwise, to acondition where the flux on the sleeve is no longer of fluent characteror cannot be rendered fluent on contact with the molten aluminum. Ingeneral, it has been found that an interval less than 40 seconds ispreferred for best results.

The low temperature limit of the flux bath given above is very importantto control in order to avoid an incomplete bond, for example, bysolidification of the molten aluminum. on contact with the ferrous metalfollowing completion of the fluxing step and contacting of the ferrousmember in the mold by the molten aluminum. If the temperature of theflux bath is substantially below about 1340, for instance 1300-l320 35.,prior to immersion, solidification on contact can occur to prevent agood alloy bond between the ferrous metal and the cast aluminum. Forexample, this may be the case where proper allowance is not made for adrop in the temperature of the bath due to immersing a cold barrel andbringing it up to the lowered bath temperature and which drop in thecase of small baths may be between 50 F. to or where there is asubstantial drop in the temperature of the barrel due to too long aninterval between dipping and pouring. Moreover, the lower temperature ofthe flux may decrease the viscosity of the flux film to a point where itis not readily washed away by the rising level of aluminum on pouringinto the mold, thus presenting a barrier between the aluminum and steelat the interface. Some deviation below 1340 F., to a temperature in theorder of 1300 F. can be tolerated,

' 33 for example, in the case where little drop occurs or if the elapsedtime between removing the ferrous body from the flux bath and pouring ofthe molten aluminum is made an absolute minimum, for instance, betweenabout to seconds by fast handling of the parts and mold and rapidpouring of the aluminum, or even as low as 1250 F. when an aluminumalloy is employed as hereinafter described.

The upper limit temperature of the flux bath is also critical. If thetemperature is too high, the resultant fiux will be too fluent and theblanket it forms on the barrel will be thin and may not completelyprevent oxidation from occurring. It would not be practical to employlarge amounts of zinc chloride at these temperatures to correct thiscondition. Moreover, in many instances the ferrous body has beenpreviously brought to a particular condition of hardness ormicrostructure by preheating and tempering, and if the temperature ofthe llux bath. is too high, sufiicient heat may be transferred to theferrous body by the flux to raise its temperature above the criticalpoint of the material such that its microstructure changes to austenite,and upon subsequent quenching, to martensite with a rmultant increasedhardening of the ferrous body. This may be the cause of tool breakage insubsequent machining operations. In general, for example, where barrelsof 28-32 Rockwell C hardness are to be muffed, an upper temperatureexceeding 1360 F. will produce a sharp increase in hard ness of mostalloy steels.

The optimum temperature range of the flux bath is also somewhatdependent upon the amount of zinc chlo ride in the composition, thisingredient, having in addition to its fluxing properties, the effect ofcontrolling the viscosity of the flux composition. For example, we haveobserved that with a new bath high in cryolite (25%) and containing byweight 25% or more zinc chloride, a commercially satisfactory aluminumalloy bond may not be obtained, if the flux bath is at a temperature of1340 F. because the resultant flux layer obtained on immersing theferrous member in the flux bath may be too thick, but that a good alloybond will be obtained if the flux bath temperature is in such cases madebetween about 1375 F. to 1400 F. or even higher, for instance, 1425 F.where the cold barrel effects a sub stantial temperature drop in thebath upon immersion. It has been further noted, however, that if theflux bath has been heated for a number of days at the highertemperature, some of the zinc chloride escapes as fumes and somecryolite settles out as the principal constituent of the sludge in thebottom of the furnace. If an appreciable reduction in the zinc chloridecontent occurs, for example, to about by weight, the thickness of theflux film formed on the ferrous members will decrease, even with thebath at a temperature of 1340 F., to a point where it may be readilywashed from the surface of the ferrous body by the molten aluminum and agood aluminum alloy bond be effected. Hence the temperature of the bathmay be thereafter lowered to 1340 F. if desired.

The optimum temperature of the flux bath is likewise influenced to someextent by the amount of cryolite present in the composition. Thisessential ingredient, which promotes wetting and dissolves oxides, hasthe further effect when used in large amounts, of mechanicallythickening the flux composition. Accordingly, a somewhat higher bathtemperature is preferred when large amounts of cryolite are employed andthe temperature of the bath may again be lowered when some of thisfluoride salt is lost, as noted above, by sludging.

Based upon our observations, the preferred temperature range for theflux bath will be between about 1330 F. and about 1400 F. (1360 F.maximum if hardening is a factor), and the preferred composition forlarge of large furnaces (600 lbs.)

scale operations will be one preferably containing the followingessential ingredients:

' Parts by weight Sodium chloride About 25 to 35 Potassium chlorideAbout 25 to 35 Natural Greenland cryolite About 9 to 20 Zinc chlorideAbout 15 to 25 .ever, that the amount of substitute cryolite in thecomposition should not exceed about 50% as the present commercial gradeof synthetic cryolite is an impure substance, and the presence of toogreat a quantity adversely affects the alloy bond between the aluminumand ferrous metal. Likewise, it is preferred in commercial operationsthat the calcium chloride be added after the previously named essentialingredients of the composition have been thoroughly mixed and chargedinto the furnace and the bath is molten. The amount added preferablywill not exceed about 2 /2 to 5 percent by weight of the total charge inthe furnace. It has further been noted that if the amount of cryolite inthe composition has been reduced substantially below about 10 percent byweight, the alloy bond between the aluminum and ferrous metal will beadversely affected and the minimum percentage of this: essentialingredient should be re-established.

As will be evident from the previous discussion of the flux composition,that the zinc chloride and cryolite contents do not remain constantduring extended operations, and a control of the composition istherefore preferably provided to compensate for losses in thecomposition due to these ingredients. Various procedures were tried. Byone method, additions of one or both of the critical ingredients, basedupon chemical analysis, were made to the bath when tests indicated thatthe content of these ingredients had dropped to a point where anunsatisfactory bond between the aluminum and the steel would beobtained. This mode of bringing the bath back to its originalcomposition was not found commercially expedient because considerableloss of zinc chloride resulted from excessive fuming when largeadditions of zinc chloride were made and because the added cryolite didnot readily go into solution and sludged heavily.

A second method employed with better results was to ladle outapproximately half of the bath content when failures of bond seemedimminent andto then restore the bath to its proper level by adding newmix to the remainder. This method was also not considered good enoughfor commercial operations.

A much improved method of control was then evolved by which dailyadditions of flux composition were made to the bath to restore its leveland character. In this connection it was found that'in a 600-poundfurnace, about 35 pounds (about 5%) of ready mixed salt were requiredeach day for makeup, primarily to correct for drag-out losses. Moreover,it was noted from accumulated chemical data, that the cryolite loss wasapproximately 2% by weight per day and that of zinc chlorideapproximately 1% by weight per day. The control effected was to add 35pounds of makeup mixture per day comprising 26 pounds of ready mixedsalt, 6 pounds of cryolite, and 3 pounds of zinc chloride. This dailyaddition efiectively counteracted the cryolite and zinc chloride lossesand provided a satisfactory bond each day of operation. The amount ofmakeup was, moreover, varied depending upon the chemical analysis of thebath, this amount sometimes exceeding the 35 pounds basic addition, inwhich case a portion of the bath was ladled out to provide a properoperating level after additions.

As a result of further observations, a still more flexible system ofcontrol requiring no ladling out of flux and facilitating a closercontrol of the composition was evolved for making up cryolite and zincchloride losses.

It was noted, for example in connection with a new 600-pound furnace,that if it was loaded with fresh salt, satisfactory bonding operationscould not be commenced during an initial 48-hour period due to seepageof salt into the porous refractory of the furnace to establish a sealand heavy sludging during this period. During this two-day period, thebath is a murky, non-translucent appearing mass. However, thereafter itchanges to a clear translucent body making visible the bottom of theelectrodes. When the latter stage is reached, it is an indicator thatsatisfactory casting operations productive of excellent bonds may beundertaken.

It was also observed that if the starting cryolite content was 25% byweight, this ingredient rapidly settled duction rates, approximately 35pounds of salt were required for makeup purposes. Employing this factorand a pre-mixed salt having substantially the following composition:

Percent by weight Sodium chloride 27 /2 Potassium chloride 27 /2 NaturalGreenland cryolite 20 Zinc chloride 25 As the starting and/ or additivemixture, the following control was evolved.

If the daily check of the flux bath showed a cryolite content between16% and 25% by weight, no addition of salt was made. Each day thecryolite content was between 12 /2% and 16% by weight, a 35pound batchof salt made up of 20%'by weight cryolite and 80% by weight of theforegoing pre-mix was added. Each day the cryolite content of the bathon checking was found to be between 11% and l2 /z%, a 35-pound batch ofsalt made up of 30% cryolite and 70% of the above pre-mix salt wasadded. If on the daily check the cryolite content fell below 11%, a35-pound batch of salt made up of 40% cryolite and 60% of the pre-mixsalt was added.

By this method of control of the cryolite constituent of the bath it wasfound that additions of zinc chloride are seldom necessary other than bythe pre-mixed makeup salt added to the cryolite when making additions ofthat ingredient. However, if the zinc chloride content dropped below 19%by weight assuming an original content of 25% by Weight, additions ofzinc chloride were preferably made as a mixture thereof with theforegoing premix salt and cryolite, and in quantities not exceeding 20%by weight of the total salt addition. This procedure for adding zincchloride restores the quantity in the bath to above 19%. Experience hasshown that such an amount produces a flux bath having better fluidity.The described method of adding zinc chloride also eliminates excessiveloss of this ingredient by smoking when the addition is made.

It will be understood that the daily addition of flux is not limited tothe 35-pound amount based upon experience with a furnace capable ofhandling a 600-pound charge of salt but that this amount may be variedas conditions show the need for greater quantities to restore the bathlevel. However, it is preferred that no greater amount than 70 pounds beadded in one day to a furnace of 600 pounds capacity and then only inbatches where the direct cryolite addition is no greater than 30%, forexperience has shown that larger direct cryolite contents may causeexcessive sludging.

By using the described control it was found possible to maintain theamount of cryolite in the bath at all times between 11% and 14% and theamount of zinc chloride between 19% and 24% and obtained a bond of thealuminum to the ferrous member in all operations. Obviously, theremainder of the bath comprised the other essential ingredients sodiumchloride and potassium chlo ride and when included such additions ascalcium chloride or other salts to the degree previously indicated.

The fiuxing of ferrous bodies by our invention may be carried out withbest results if the surface of the ferrous metal is roughened, forexample, by grit blasting to obtain a larger surface area of the ferrousmetal for exposure to the flux and consequently to the aluminum therebymaking a stronger bond possible. Moreover, with such a greater surfacearea of roughened character, there is less tendency for the fluent fluxto run off or to become too thin during the casting procedure,particularly in the interval between completion of the fiuxing step andpouring of the molten aluminum. It will be understood, however, thatgood bonds may be obtained by the processes described herein Withoutgrit blasting by using either ground or turned surfaces.

It may also be noted that one of the critical aspects of the processingis the temperature of the sleeve at which the molten aluminum makescontact with the steel surface. It is difiicwlt because of manyvariables present to determine this temperature and hence in theforegoing description other temperature indicators have been employed.However, it is believed that the temperature of the sleeve should be oneat least above the melting point of the aluminum (1220 F.) and may serveas an additional control guide.

Prior to starting casting operations it is also preferred that the moldsbe preheated as by gas torch to between 500-700 F. This does not have tobe repeated once casting has begun as enough heat remains in the moldsafter casting without again preheating. The molds are also preferablycleaned after each casting operation by blowing off with a light streamof water. The steam formed by this application of water seems to breakaway the salt accumulation on the side walls of the mold and provides abetter operation than that obtained with a mold wash, for instance ofthe graphite type. In fact the use of a stop-off paint such as pyro atthe tops of the barrels to prevent bonding of the aluminum is also foundto be unnecessary, as any excess aluminum at the top of the casting canbe machined off and no difiiculty experienced even at the bond where anend feed tool is used to cut below the aluminum-steel interface. Thehard brittle Fe-Al compound at the bond breaks up ahead of the edge ofthe cutting tool.

For a number of reasons, it is often desirable to start cooling of themuffed cylinders after pouring of the aluminum has begun. This isaccomplished by an airwater vapor spray directed against the interior ofsuch cylinders. This cooling promotes directional solidification of thealuminum and thereby avoids shrinkage cavities. Moreover, such coolingprevents distortion of the ferrous metal and aids in maintaining aproper hardness level where such is necessary. In the latter connection,if the part is not cooled, heat imparted by the molten metal maymaintain its temperature within the tempering range for a sufficienttime to decrease the hardness of the previously hardened ferrous memberto a degree below its desired hardness specification.

Where it is desired to provide a longer cooling period for the moltenaluminum after pouring in which it remains in a molten condition so thatthe flux may be more readily completely displaced before the aluminumsolidifies, a lower melting point aluminum composition may be used. Sucha composition may be obtained by the addition of silicon, tin or otherelements. For example, when used in amounts approximately 11% by weightof the composition, silicon will provide a melting point as low as 1070F. Lesser amounts will, of course, determine the temperature for amelting point between 1070 F. and 1220 F. The use of silicon in thealuminum melt has a further advantage of providing a thinner andstronger alloy bond between the cast layer and the ferrous metalsurface. For the purpose of giving those skilled in the art some betterunderstanding of the possibilities of our invention, the followingillustrative examples are given:

Example I Sodium chloride (NaCl) 24.5 Potassium chloride (KCl) 24.5 Zincchloride (ZnCl 24.5 Natural Greenland cryolite (Na AlF 24.5 Calciumchloride (CaCI 2.5

When the sleeve reached the temperature of the bath, it was immediatelyremoved and placed in a steel mold of a size to form upon casting analuminum muff thick and 4" long at one end of the sleeve. Within 31seconds of removal of the sleeve from the bath, molten aluminum of about1220 F. melting point and at a temperature of 1400 F. was poured intothe mold around the sleeve. The cast member was then permitted to aircool. Visual and microscopic examination of the alloy bond between thealuminum and steel disclosed that an excellent alloy bond was obtained.It was also evident there had been excellent wetting of the steel, andthat the alloy bond was continuous, complete and free of any flux oroxide inclusions.

Example 11 A steel sleeve of the character described in Example I wasprovided with a cast aluminum muff as there described, the molten fluxbath in this example being maintained at a temperature of about 1350 F.The composition of the bath was substantially as follows:

Parts by weight Sodium chloride 40 Potassium chloride 40 NaturalGreenland cryolite 20 Example III An aluminum muff was cast about asteel sleeve of the character described in Example No. 1 and in themanner there stated, the flux being maintained at 1400 F., and themolten aluminum having a melting point of about 1220 F. and a workingtemperature of about 1400 F. The composition of the flux bath wassubstantially as follows:

' Parts by weight Sodium chloride 7 Potassium chloride 44 Zinc chloride34 Natural Greenland cryolite 15 About 24 seconds was utilized forpouring.

The time interval between removal of the sleeve from the flux bath andthe start of pouring was 30 seconds, and the pouring time was 10seconds. Visual and microscopic examination disclosed a good bond andgood Wetting.

Example IV A steel sleeve of the size described in Example I was fluxedand provided with a cast aluminum mufi in the manner there stated, usinga flux bath maintained at a temperature of 1400 F. and molten aluminumhaving a melting point of 1220 F. and a working temperature of about1400 F. The composition of the flux bath was substantially as follows:

Parts by weight Sodium chloride 25 Potassium chloride 25 Zinc chloride25 Natural Greenland cryolite 25 The time interval between removing thesleeve from the flux bath and start of pouring was 30 seconds. Thepouring time was 13 seconds. Visual and microscopic examinationdisclosed good wetting and an excellent alloy bond.

Example V A steel sleeve of the character described in Example I wasprovided with a coating of flux and a cast alummum mufl in the mannerthere stated, the flux bath being maintained at a temperature of 1300 F.and the molten aluminum having a melting point of about 1220 F. and aworking temperature of about 1400 F. The composition of the flux bathwas substantially as follows:

Parts by weight Sodium chloride 35 Potassium chloride 35 Zinc chloride15 Natural Greenland cryolite 15 The elapsed time between removal of thesleeve from the bath and the start of pouring was 11 seconds, and thepouring time was 8.5 seconds. Visual and microscopic examinationdisclosed a good alloy bond of about .001 thickness.

Example VI A steel sleeve of the character described in Example I wasfiuxed and provided with a cast aluminum muff as there describedutilizing a flux bath at a temperature of about 1400 F. and moltenaluminum having a melting point of about 1220 F. at a workingtemperature of about 1400 F. The flux composition was substantially asfollows:

- Parts by weight Sodium chloride 35 Potassium chloride 35 Zinc chloride15 Natural Greenland cryolite 15 The elapsed time between removal of thesleeve from the flux and the start of pouring was 30 seconds, and thepouring time was 10.5 seconds. Visual and microscopic examinationdisclosed a good alloy bond having about .001" thickness.

Example VII sleeve. The flux bath had substantially the followingcomposition:

Parts by' weight Sodium chloride 25 Potassium chloride 25 Zinc chloride25 Natural Greenland cryolite 25 A steel barrel of the character of thepreceding example was immersed and heated in a molten flux bathmaintained at 1350 F. in an Ajax submerged electrode salt bath furnacehaving a capacity of 600 lbs. of salt. The flux had substantially thefollowing composition:

Parts by weight Potassium chloride 35 Sodium chloride 35 Zinc chloride19 Natural Greenland cryolite 11 As soon as the sleeve reached thetemperature of the bath, which required about 3 minutes immersiontherein, it was immediately removed and placed in a steel mold fixtureinto which molten aluminum having a melting point of about 1220 F. and aworking temperature of about l350 F. was poured within 20 seconds of thetime the sleeve was removed from the bath, the pouring time being about8 seconds. An excellent alloy bond was obtained.

Example IX A shouldered steel barrel of about diameter with a wallthickness of about 7 inch, a /3 inch flange and a length of about /2inches was sand blasted in a Wheelabrator cabinet on its exteriorsurface area to which an aluminum muff is to be cast. It was then placedin a Detrex" degreaser to remove any grease, and following this paintedwith a Pyro paint to protect the areas to which the aluminum was not tobond.

The barrel was then immersed in a flux bath of molten salt fiux heatedto a temperature of 1400 to 1425 F. in an immersed electrode Ajaxelectric salt bath furnace of 185 lbs. capacity and kept immersed for 3/2 minutes. The temperature of the barrel at the elapsed time, asdetermined by a thermocouple attached to the side wall of the barrelduring immersion, was between 1340 to 1360 F. There was a drop of 50 to75 F. in the bath temperature experienced on immersion.

The fiux bath was prepared by thoroughly mixing to gethcr substantially:

Parts by weight Sodium chloride 25 Potassium chloride 25 Zinc chloride25 Natural Greenland cryolite 25 and charging the same into the furnace.After the bath was molten, approximately 2 /2% of calcium chloride basedon the weight of the total charge was added.

The flux treated barrel after heating to the abovestated temperature wasthen removed from the hot salt fiux and placed in a metallic moldfixture preheated to 500-700 F. and constructed to enable an aluminummuff about 6" long and 1%" thick and weighing about 19 lbs. to be castaround the barrel. Molten aluminum at a temperature between 1325 and1350 F. prepared from 99% pure ingot having a melting point of about1220' F- was immediately poured in the mold by hand ladles to a heightof 6 /2". Pouring of the aluminum was started within 25 seconds from thetime the barrel was removed from the hot salt flux and pouring continuedas rapidly as possible until the mold was topped. About 10 seconds wasrequired for filling the mold. An operator stood by with a ladle ofaluminum to fill in any shrinkage cavities developed duringsolidification of the aluminum.

During pouring commencing when the mold was half filled, the barrel wasair-water cooled by an air-water vapor spray directed against the insidethereof. After the aluminum solidified, the barrel was removed from thefixture and quenched. in. oil. Examination of the bond disclosed it tobe excellent.

Example X A shouldered steel barrel of about 5%" inside diameter andbetween to wall thickness and a length of about 10 /2, was roughmachined from forgings of an SAE 8640 or AISI TS-8640 or SAE 4140 steeland heat treated, austenitized, quenched in oil, and tempered to ahardness of 28' to 32 Rockwell C. The barrel was then cleaned in a Mahonwasher to remove any grease or dirt, then shot blasted in a blastcabinet to blast clean the outside of the barrel and remove any shinefrom the surfaces to be aluminum muffed.

The barrel was immersed in a flux bath of molten salt flux heated to atemperature between 1330 F. and 1350 F. preferably 1340 F. in animmersed electrode Ajax electric salt bath furnace of 600 lbs. capacityand kept immersed for 3 minutes. The flux bath was prepared from ahomogeneous mixture of substantially the following ingredients insubstantially the amounts stated, these ingredients being in granularform of 50 to 200 mesh and of 99% plus purity:

Parts by weight Potassium chloride 27 /2 Sodium chloride 27 /2 Zincchloride 25 Natural Greenland cryolite 20 After the bath was molten,approximately 2 /2 by weight of calcium chloride, based upon the weightof the total charge, was added.

The flux-treated barrel was then removed from the hot salt flux andpromptly placed in a preheated Huckins mold fixture previously heated toa temperature between 500 to 700 F. and constructed to enable analuminum muff about 6" long and 1% thick, and weighing about 19 lbs. tobe cast around the barrel. Molten alurnimun at a temperature between1315 F. and 1335 F. prepared from 99% pure ingot having a melting pointof about 1220 F. was immediately poured into the mold with hand ladiesto above the mull area and topped to prevent shrinkage cavities in themull. Air-water cooling of the inside of the barrel was commenced duringpouring, by an air-water spray applied to the inside of the barrel whenthe mold was filled to a height of 2" to 3 of aluminum. Pouring of thealuminum was commenced promptly, i.e., between 10 to 20 seconds afterthe barrel was removed from the salt flux bath (the average for a runwas 15 seconds) and pouring made continuous during the entire pouringcycle. The time to fill the mold with molten aluminum was between 6 to10 seconds (the average for a run was 8 seconds), this time interval notincluding the time required for topping oil the mold. The air-waterspray cooling was provided by a movable spray head operating with an airline pressure of 30 to 40 pounds per square inch, and arranged to moveupwardly in the barrel at a rate to require between 2% to 2 /2 minutesto move over the cast area. The rate of water flow in the head wasadjusted such that no actual streams of water were ejected from thespray head, but rather the water was in the form of vapor. Moreover,

the head was adjusted so that the vapor was not excessive 13 to theextent of spraying over into the molten aluminum on pouring.

After the aluminum had solidified, the barrel was removed from the moldand quenched in tap water.

Examination of the cast muff showed an excellent continuous bond formedwith the steel barrel.

From the above description of our invention and examples, it will beevident that various modifications and substitutions will be obvious andothers will readily suggest themselves to those skilled in the art, allhowever without departing from the spirit and scope of our invention.

We claim:

1. In a process of producing a duplex metal structure comprising ahollow ferrous metal body and a cylindrical cast aluminum mufi having analloy bond therewith comprising positioning said body in a moldproviding a cavity adjacent said body shaped to form said muff, pouringmolten aluminum into said cavity to form said muff, and directing anair-Water vapor spray against the interior of said body after startingpouring of the aluminum but before it has been completed.

2. In a process of producing duplex metal structures comprising acylindrical ferrous metal body and a surrounding cast aluminum muffhaving an alloy bond therewith comprising positioning said body in amold providing a cavity adjacent the outer cylindrical surface of saidbody shaped to form said muff and providing access to the interiorcylindrical surface of said body, pouring molten aluminum into saidcavity, to form said muff, after commencing pouring directing a ring ofair-water vapor against the interior cylindrical surface of said bodyopposite the poured aluminum and movingsaid ring of vapor through thearea of contact of. said molten aluminum and in step with said pouring.

3. The process of producing a duplex metal structure comprising acylindrical heat hardened ferrous metal body and a supporting castaluminum body having an alloy bond therewith, comprising immersing saidferrous body in a bath of fluent molten flux having a temperaturebetween 1250 F. and 1450 F. and consisting essentially of cryolite andchlorides, maintaining said body in said bath for a time intervalsuflicient to provide said body when withdrawn therefrom with acontinuous layer of said fluent flux on the portion of said ferrous bodywhere it is to be bonded with said aluminum, withdrawing said ferrousbody from the flux bath, positioning the flux layered ferrous body in amold providing a cavity adjacent said ferrous body shaped to form saidaluminum body, pouring molten aluminum at a temperature between 1325 F.and 1425 F. into said cavity while said flux of said flux layer is stillfluent, to form said aluminum body, said molten aluminum displacing saidfluent flux ahead of it in the cavity and forming when set a ferroaluminum alloy bond with said ferrous body, directing a ring of airwater vapor against the surface of said ferrous body opposite the pouredaluminum during pouring thereof and moving said ring of vapor throughthe area of contact of said molten aluminum and substantially in stepwith said pouring.

4. The process of producing a duplex metal structure comprising acylindrical heat hardened ferrous metal body and a supporting castaluminum body surrounding said ferrous metal body and having an alloybond there with, comprising immersing said ferrous body in a bath offluent molten flux having a temperature between 1250 F. and 1450 F. andconsisting essentially of cryolite and chlorides, maintaining said bodyin said bath for a time interval sufficient to provide said body whenwithdrawn therefrom with a continuous layer of said fluent flux on theportion of said ferrous body where it is to be bonded with saidaluminum, withdrawing the said ferrous body from the flux bath,positioning the flux layered ferrous cylindrical surface of said ferrousbody shaped to form said aluminum body, providing access to the interiorcylindrical surface of said ferrous body, pouring molten aluminum at atemperature between 1325 F. and i1425 F. into said cavity while said fim of said liux layer is still fluent to form said aluminum body, saidmolten aluminum displacing said fluent flux ahead of it in the cavityand forming when set a ferro aluminum alloy bond with said ferrous body,following start of pouring of said aluminum directing a ring of airwater vapor against the interior cylindrical surface of said ferrousbody opposite the poured aluminum and moving said ring of vapor throughthe area of contact of said molten aluminum and substantially in stepwith said pouring.

5. The process of producing a duplex metal structure comprising a heathardened ferrous metal body and a cast aluminum body having an alloybond therewith, comprising immersing said ferrous body in a bath offluent molten flux having a temperature between 1250 Fpand 1450 F. andconsisting essentially of cryolite and chlorides, maintaining saidferrous body in said bath for a time interval sufiicient to provide saidferrous body when withdrawn therefrom with a continuous layer of said'fluent flux on the portion of said ferrous body where it is to becomebonded with said aluminum, withdrawing said ferrous body from the fluxbath and immediately positioning the flux layered ferrous body in a moldproviding a cavity adjacent said ferrous body shaped to form saidaluminum body and then substantially immediately pouring molten aluminumat a temperature between 1325 F. and 1425 F. into said cavity while saidflux of said flux layer is still fluent to form said aluminum body, saidmolten aluminum displacing said fluent flux ahead of it in the cavityand forming when set a ferro aluminum alloy bond with said ferrous body,and during said pouring of aluminum directing a spray of air water vaporagainst the surface of said ferrous body opposite that contacting saidaluminum.

6. The process of producing a duplex metal structure comprising aferrous metal body and a facing of cast aluminum alloy having an alloybond therewith, comprising immersing said body in a bath of fluentmolten flux consisting essentially of fluorides and chlorides and havinga temperature above the melting points of the flux and aluminum alloyand not exceeding substantially 1450 F., maintaining said body in saidbath for a time interval sufficient to provide said body when withdrawntherefrom with a continuous layer of said flux on the portion of thebody where it is to be aluminum faced, said body when withdrawntherefrom being in a heated condition and said flux thereon beingfluent, withdrawing said body from the said flux bath and positioningthe flux layered body in a mold providing a cavity adjacent said bodyshaped to form said facing, while said flux of said flux layer is stillfluent casting between said body and said mold a facing of moltenaluminum alloy at a temperature above its melting point and notsubstantially exceeding 1425 F., said molten aluminum displacing saidfluid flux ahead of it in the cavity and forming when set aferro-aluminum alloy bond with said body, and directing an air Watervapor spray against the surface of said ferrous metal body opposite thatto which the aluminum is cast during filling of said cavity with moltenaluminum but after filling has started.

References (Iited in the file of this patent UNITED STATES PATENTS492,874 Reusch Mar. 7, 1893 2,131,062 McBride Sept. 27, 1938 2,245,578Enderich June 17, 1941 2,284,729 Dusevoir June 2, 1942 2,544,671 GrangeMar. 13, 1951 2,611,163 Schaefer Sept. 23, 1952 2,715,252 Schaefer Aug.16, 1955 2,881,491 Jominy Apr. 14, 1959

3. THE PROCESS OF PRODUCING A DUPLEX METAL STRUCTURE COMPRISING ACYLINDRICAL HEAT HARDENED FERROUS METAL BODY AND A SUPPORTING CASTALUMINUM BODY HAVING AN ALLOY BOND THEREWITH, COMPRISING IMMERSING SAIDFERROUS BODY IN A BATH OF FLUENT MOLTEN FLUX HAVING A TEMPERATUREBETWEEN 1250*F. AND 1450*F. AND CONSISTING ESSENTIALLY OF CRYOLITE ANDCHLORIDES, MAINTAINING SAID BODY IN SAID BATH FOR A TIME INTERVALSUFFICIENT TO PROVIDE SAID BODY WHEN WITHDRAWN THEREFROM WITH ACONTINUOUS LAYER OF SAID FLUENT FLUX ON THE PORTION OF SAID FERROUS BODYWHERE IT IS TO BE BONDED WITH SAID ALUMINUM, WITHDRAWING SAID FERROUSBODY FROM THE FLUX BATH, POSITIONING THE FLUX LAYERED FERROUS BODY IN AMOLD PROVIDING A CAVITY ADJACENT SAID FERROUS BODY SHAPED TO FORM SAIDALUMINUM BODY, POURING MOLTEN ALUMINUM AT A TEMPERATURE BETWEEN 1325*F.AND 1425*F. INTO SAID CAVITY WHILE SAID FLUX OF SAID FLUX LAYER IS STILLFLUENT, TO FORM SAID ALUMINUM BODY, SAID MOLTEN ALUMINUM DISPLACING SAIDFLUENT FLUX AHEAD OF IT IN THE CAVITY AND FORMING WHEN SET A FERROALUMINUM ALLOY BOND WITH SAILD FERROUS BODY, DIRECTING A RING OF AIRWATER VAPOR AGAINST THE SURFACE OF SAID FERROUS BODY OPPOSITE THE POUREDALUMINUM DURING POURING THEREOF AND MOVING SAID RING OF VAPOR THROUGHTHE AREA OF CONTACT OF SAID MOLTEN ALUMINUM AND SUBSTANTIALLY IN STEPWITH SAID POURING.